Regula S. Briellmann

Functional connectivity networks are disrupted in left temporal lobe epilepsy

Functional connectivity maps the distributed network of brain regions fluctuating synchronously during a continuous brain state. This study sought to investigate whether patients with left temporal lobe epilepsy (TLE) differ from controls in their resting‐state functional connectivity between typical language regions.

Seizure-associated hippocampal volume loss: a longitudinal magnetic resonance study of temporal lobe epilepsy.

This longitudinal quantitative magnetic resonance imaging study of 24 patients with mild temporal lobe epilepsy shows an ipsilateral hippocampal volume decrease of 9% (range, −30 to +0.5%; p = 0.002, paired t test) over a period of 3.5 ± 0.7 years. The hippocampal volume loss was correlated to the number of generalized seizures between the scans (p = 0.0007, r = 0.6), suggesting seizure‐associated hippocampal damage.

Hippocampal pathology in refractory temporal lobe epilepsy: T2-weighted signal change reflects dentate gliosis.

Background: The MR and pathologic features of hippocampal sclerosis (HS) are well described and include volume decrease and T2-weighted signal increase for MRI, and neuron cell loss and gliosis for pathology. Objective: To confirm the established correlation between hippocampal volumes and neuron cell counts, and to study the still controversial association between signal change and gliosis. Methods: The authors studied 44 patients (22 men and 22 women; mean age at surgery, 37 years) with refractory temporal lobe epilepsy. Quantitative assessment of hippocampal volumes and T2 relaxometry, and neuron and glial cell count in the region CA1 and molecular layer of the dentate gyrus was performed. The proportion of glial fibrillary acidic protein (GFAP)-positive glial cells (reactive astrocytes) was indicated. Results: In a stepwise regression, the ipsilateral hippocampal volume was predicted best by the neuron cell count in the dentate gyrus (p = 0.005, r = 0.4). Hippocampal T2 time, however, was predicted best by the glial cell count in the dentate gyrus (p = 0.01, r = 0.4). None of the other cell counts contributed to either model. In the dentate, 31% of the glial cells were reactive astrocytes, whereas in CA1, 5% were reactive. Conclusion: The results confirmed the correlation between hippocampal volumes and neuron cell counts. T2-weighted signal increase in the hippocampus was mainly influenced by gliosis in the dentate gyrus, where a high proportion of glial cells show abnormal activity. This activity may reflect changes important in the development of hippocampal epileptogenicity.

Seizure-associated abnormalities in epilepsy: evidence from MR imaging.

Summary:  Acute seizure‐associated changes have been described in the animal and human literature. Controversy exists over whether seizures cause permanent damage to the brain, and whether a (prolonged) seizure can induce changes that lead to an epileptic lesion, resulting in habitual seizures and epilepsy. Current magnetic resonance imaging (MRI) offers a variety of imaging tools and is capable of detecting acute seizure‐associated changes. In contrast to the histologic examination, serial MRI studies are possible and allow longitudinal observation of the fate of these changes. This report reviews the literature on acute seizure‐associated effects emphasizing the MRI evidence.

Hippocampal sclerosis studied in identical twins

Objective: To test both the genetic and acquired hypotheses for the etiology of hippocampal sclerosis (HS) by studying with optimized and quantitative MRI three monozygous (MZ) twin pairs in which the index twin had temporal lobe epilepsy and HS. Background: There is conflicting evidence in the literature regarding whether HS is genetic or acquired prenatally, perinatally, or as a consequence of prolonged childhood seizures. Methods: We compared three MZ pairs with 30 age-matched control subjects who had no history of a neurologic disorder; we also used the twins as matched samples to assess subtle differences between the affected and unaffected twins. Results: All of the affected twins had prolonged seizures with fever in early childhood, which stood out as the unique factor common to all affected twins and was absent in all the unaffected twins. HS was present in all affected twins but was absent in the unaffected twin on visual, volumetric, and T2 relaxometry criteria. Comparison of the affected twin with the co-twin revealed that intracranial volume ipsilateral to the HS was relatively small in two of three affected twins. Conclusions: The absence of HS in the unaffected twin is strong evidence against a genetic hypothesis for HS. Neither perinatal problems nor birth order were factors in determining the presence of HS. This twin study supports the notion of HS as an acquired lesion secondary to prolonged seizures in early childhood and suggests that regional abnormalities of intracranial volume are associated with HS.

Spike-triggered fMRI in reading epilepsy Involvement of left frontal cortex working memory area

Objective: To determine the origin of epileptiform activity in reading epilepsy (RE) and the association between these regions and regions activated by reading, and to assess brain morphometry in these areas. Methods: In two subjects with RE, EEG was recorded inside the three tesla MRI while subjects read silently. Spike-triggered fMRI images were compared to baseline. In a second fMRI study, 30 seconds of silent reading was compared to visual fixation. Morphometry of these areas was assessed using curvilinear surface reconstruction. Left central sulcal patterns in three subjects with RE were compared to three subjects with idiopathic generalized epilepsy (IGE) and 12 normal controls. Results: One subject with RE showed spike-related activity (17 spikes) in the left precentral gyrus, and bilaterally in the central sulcus and globus pallidus. The other showed no definite activation owing to low spike numbers (4 spikes). In both subjects, the block reading task recruited normal visual and language areas including the left posterior middle frontal gyrus. Two subjects with RE showed an unusual gyrus branching anteriorly off the left central sulcus. A similar sulcal pattern was seen in none of the subjects with IGE and only 1 of 12 controls. Conclusion: Spike activity overlapped with reading activity in the left middle frontal gyrus, a structure recruited during working memory cognitive tasks. The authors postulate that, because of a local structural anomaly, the spikes of reading epilepsy spread from working memory areas into adjacent motor cortex, activating a cortical subcortical circuit.

Thalamic Atrophy in Childhood Absence Epilepsy

Summary:  Purpose: Patients with childhood absence epilepsy (CAE) have normal clinical magnetic resonance imaging (MRI) studies. The presence of abnormalities in corticothalamic networks has been suggested to be the functional basis of absence seizure generation. We assessed whether structural grey and white matter volume changes of these areas occurred in patients with absence seizures by using optimized voxel‐based morphometry (VBM).

Voxel-based relaxometry: a new approach for analysis of T2 relaxometry changes in epilepsy.

The measurement of the T2 relaxation time (T2 relaxometry) had been established as a reliable tool for the assessment of certain conditions such as temporal lobe epilepsy. The standard procedure for analysis of T2 data uses manually drawn regions of interest (ROIs). This approach is limited by its subjective nature and its restricted scope of investigation within selected regions of the brain. In this study, we introduce a voxel-based analysis approach termed voxel-based relaxometry (VBR). Tissue signal changes were assessed in 19 patients with hippocampal sclerosis (HS) and in 38 healthy controls using (i) conventional ROI-based analysis with several bilateral ROIs and also (ii) the VBR method in which the T2 maps are warped to a stereotactic space, smoothed and statistically compared. Conventional ROI analysis identified the expected T2 increase in the sclerotic hippocampus in all HS patients. Furthermore, 13 of the 19 patients displayed a T2 increase in at least one of the other ROIs. The VBR analysis showed a similar pattern of statistically significant areas of increased T2 within the sclerotic hippocampus. In addition, extrahippocampal areas of increased T2 were apparent including the anterior temporal lobe white matter and the parahippocampal gyrus. The results of the VBR analysis are in agreement with the conventional ROI analysis. The VBR analysis has the advantage of providing an even-handed assessment of T2 differences through the brain. We recommend VBR as an alternative means of relaxometry data analysis that provides an objective assessment of differences between subjects.

Men may be more vulnerable to seizure-associated brain damage

Background: Repetitive seizures may be associated with progressive neuronal damage measurable by quantitative MRI. Objective: To investigate whether gender is a risk factor for this damage. Methods: Sixty patients with refractory temporal lobe epilepsy (TLE) (28 men, 32 women) and 54 healthy controls (28 men, 26 women) were compared by quantitative MRI methods. Results: Male patients had ipsilateral hemicranial volume loss of 12% (CI 8% to 16%) and contralateral volume loss of 7% (CI:3% to 11%) compared with male controls (p ≤ 0.004, analysis of variance). Female patients were 4% (CI:0.3% to 8%, p = 0.04) smaller than controls in the ipsilateral hemicranium, and not different contralaterally. The patient-to-control difference was greater in men than in women for the ipsilateral (p = 0.003) and contralateral hemicranial volume (p = 0.02). In men, 14% of the ipsilateral (F = 4.7, p = 0.004) and 16% of the contralateral (F = 5.1, p = 0.03) hemicranial volume loss could be attributed to generalized tonic clonic seizures. Compared with controls, patients averaged a 29% smaller ipsilateral and a 5% smaller contralateral hippocampus. Conclusion: Men with TLE have more brain atrophy than women with TLE. Seizure frequency is a factor contributing to reduced brain volumes in men but not in women. Men, therefore, may be more vulnerable to seizure-associated brain abnormalities.–1485

Optimized clinical T2 relaxometry with a standard CPMG sequence

To optimize the accuracy and precision of T2 measurements using the standard Carr‐Purcell‐Meiboom‐Gill (CPMG) sequence. T2 values obtained with this technique are normally sensitive to imperfect refocusing due to the formation of unwanted stimulated echoes.